It is known that positioning of the propeller blades with a correct and suitable angle of incidence with respect to the fluid that strikes the blades, that is, a correct fluid dynamic pitch, makes it possible, also as a function of the conditions of use and of the torque supplied by the motor of the boat to which the propeller is coupled, to maintain a high output and achieve satisfactory performances of the same propeller.
The Italian patent IT 1 052 002, in the name of Massimiliano Bianchi, relates to the production a propeller, particularly for use in sailing boats, in which the drive shaft (or the relative propeller hub) and the propeller casing are mutually coupled by two coplanar teeth orthogonal to the propeller axis itself.
When the propeller is stationary, the blades are arranged in the feathered position, so as to generate minimum resistance, and the teeth of the hub and of the propeller casing are spaced apart so that the subsequent rotation of the drive shaft and consequently of the hub, both in one direction and in the other, determines idle rotation thereof for a given angular interval, which, due to an appropriate kinematic mechanism with pinion and gear wheels, corresponds to a rotation of the blades with respect to the cylindrical casing.
When the hub reaches the position of abutment against the propeller casing, and their relative rotation is prevented, the blades are positioned according to a predetermined fluid dynamic pitch, which will depend on the angle of relative rotation between the hub and the propeller casing, and vice versa.
In this way, the propeller blades can reach a first pitch, and consequently a given angle of incidence, adapted for forward movement of the boat, and a second pitch, adapted for reverse movement of the boat, depending on the direction of rotation of the drive shaft with respect to the propeller casing.
However, with a propeller of the type described above it is not possible to easily modify the fluid dynamic pitch, or the interval of fluid dynamic pitches, of the propeller established in the design phase.
In fact, once the pitch of the blades most suitable for forward movement and most suitable for reverse movement of the boat has been established in the design phase, it is no longer possible for the operator to easily vary this angle of rotation. Modification of the pitch of the propeller in this case can only take place by disassembling the propeller and performing internal operations either replacing the hub or the propeller casing, or subjecting these elements to machining operations.
Only by performing these operations, the relative rotation of the hub with respect to the propeller casing determines positioning of the blades at the pitch desired according to the requirements of installation and use. Naturally, the user of the propeller is not able to disassemble the propeller, or to replace or machine its parts, and therefore must have this performed by a skilled mechanic or send the propeller to the manufacturer.
To overcome these drawbacks, propellers have been developed in which the angle of relative rotation of the hub with respect to the propeller casing, and vice versa, which results in a rotation of the blades about their pivot axis with respect to the propeller casing by means of a specific kinematic mechanism, can be modified by the user by acting on threaded grub screws which are screwed into specific seats provided in the propeller, in such a manner as to project inside the propeller casing to determine a modification of the angle of relative rotation between the hub and the propeller casing.
A propeller of this type is described in the patent DE3901672, in which the hub has a tooth destined to come into contact with two relative stop abutments provided on the cylindrical propeller casing following idle rotation, for an angular interval of rotation between the propeller casing and the hub, which causes the predetermined fluid dynamic pitch of the blades to be reached.
The propeller casing is provided with two threaded seats, screwed inside which are two grub screws destined to project inside the propeller casing and on which the tooth of the hub is destined to reach the position of abutment. Consequently, the ends of the grub screws projecting inside the propeller casing form the aforesaid stop abutments for the tooth of the hub.
Relative rotation of the hub with respect to the propeller casing, and the fluid dynamic pitch of the blades that is set as a consequence, are modified by the user of the boat by screwing or unscrewing the grub screws in such a manner that the portion thereof that projects inside the propeller casing is increased or decreased, obtaining a corresponding modification of the position of abutment with the tooth of the hub, and therefore a consequent modification of the angular interval of rotation of the hub with respect to the propeller casing, and vice versa.
However, this type of propeller has some drawbacks deriving from the fact that adjustment of the pitch of the blades is obtained in a manner that is not accurate and substantially linked to the ability and precision of the user of the boat during screwing or unscrewing of the grub screws in the corresponding threaded seats for a given number of turns, or fractions of turns, suitable to reach the required pitch.
In fact, when the user of the boat wishes to modify the pitch of the blades he or she must act manually on the grub screws, screwing or unscrewing them inside the threaded seats.
Naturally, this adjustment is somewhat imprecise and the user often makes mistakes in adjusting the grub screws, which result in incorrect positioning of the blades at a different fluid dynamic pitch to the one required. In fact, as already stated, the user must perform a clockwise or counter-clockwise rotation of the grub screws for a given number of turns, or fractions of turn.
Added to this is the significant complication caused by the fact that these operations to adjust the grub screws are generally carried out under the surface of the water.
It is clear that a procedure of this kind requires numerous attempts, during which the user is required to go underwater and try various adjustments, unscrewing or screwing the grub screws.
It must also be noted that in the case in which the new fluid dynamic pitch set is not satisfactory in terms of efficiency and performance with respect to the one previously set, the user must try to remember the direction and degree of rotation of the grub screws, trying to return them to the previous position, in order to restore the previously set fluid dynamic pitch.
Therefore, it is necessary to simplify the adjustment operations described above, reducing the number of attempts that the user of the boat must carry out to obtain the required fluid dynamic pitch.
The object of the present invention is therefore to overcome the problems of prior art discussed briefly above, and to provide an assembly and related method for adjusting the fluid dynamic pitch of the blades which is simple to perform and, above all, ensures that the fluid dynamic pitch required is accurately set.
The object of the present invention is also to provide an assembly and a method for adjusting the fluid dynamic pitch thanks to which the user of the boat can position the blades at different fluid dynamic pitches without having to make numerous attempts at adjustment.